How does a compressor stall affect the operation of a gas turbine?

In summary: If the damage is catastrophic, the engine will usually not start, or it may start but rapidly lose power.
  • #1
koolraj09
167
5
Hi,
I went through many resources but I am not able to understand as to what stall/surge means for an axial compressor means. I am not able to imagine or correlate it. I want to physically understand what happens in a compressor when it is stalled. For eg: Can a ceiling fan stall when the angle of its blades it too large? If yes then what would happen in practice (things which we can observe when the fan stalls??)
An observable analogy is what I want..

Also why is stall so detrimental..this in an interlinked question (related to understanding of stall) but still I would go ahead and ask it.

In addition are there any good resources which would provide a clear understanding of things like compressor map, performance etc...

Thanks...
 
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  • #2
The individual blades are airfoils, so I think you should focus attention on the angle of attack and the stall of an airfoil. While fluid flow is laminar the airfoil will have lift but when the fluid breaks away from the surface the airfoil will stall. If there is insufficient angle of attack, the airfoil will not transfer energy to the fluid. When the airfoil has an extreme negative angle of attack, the lift will be reversed and will tend to block the flow of fluid.

It is possible for the flow through a multi-stage compressor to become unstable and oscillate between these extreme situations.
Standing or traveling waves of high and low pressure or flow can propagate along the stages.
 
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  • #4
Hi Baluncore and Spinnor..thanks for your replies..but i am still not able to clearly get what physically happens when one says the compressor is stalling/stalled?
 
  • #6
Hi..Yes I understand what is angle of attack and stall...But what exactly happens when a boundary layer separation occurs? how the fluid moves then? how the blades and vanes react at this particular moment when boundary layer is detached?
My question is there any analogy or something which could help me visualize/imagine this phenomenon.
 
  • #7
The video below is very basic but may make something click. The one wiki article mentioned that when this happens the solution is to reduce fuel flow to the combustion chamber. I would ask myself what happens as fuel flow to the engine is raised above normal maximum flow rates?



Also see,

https://www.youtube.com/results?search_query=Jet+engine+compressor+stall
 
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  • #8
Before you get into the complexities of turbine stall, I think you should focus on understanding the airfoil stall situation.
 
  • #9
As you lose laminar flow across the compressor blades that stage can no longer keep up enough pressure differential to keep the air flow along the engine, as that happens the air on the HP side of the stage reverses it's flow. A poor analogy but think what happens if you put your finger over the end of a bicycle pump, as you move the piston down you need to increase the pressure on the handle, if you release the handle it springs back.
 
  • #10
Thanks Jobrag..
It was really helpful...
 
  • #11
Nope..still confused...How does the air move when the compressor stalls? It separates from the individual or a group of airfoils...but what does it do after that? How does it move in the compressor annulus?
What happens to the airflow after the compressor stalls? Does it still go in, moving at same speed or it slows down...or it remains there as such in the compressor, stationary (if we block the air from the combustion chamber)?
How does the mass flow rate gets affected? What about the pressure ratio..how does it vary?
 
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  • #12
Two or three things happen,
First, there is huge surge in vibration, so the engine trips (stops) on high vibration.
Second, because there's a massive reduction in airflow through the hot end EGT spikes enormously and the engine trips on high temperature trip.
Third if your unlucky the reverse flow on the turbine blades rips them out of their mountings and the engine is wrecked.
 
  • #13
An axial flow compressor with a high compression ratio is potentially an unstable air flow through a pipe. The only thing that keeps the flow stable is that you continuously force air into the inlet, and its only option is to escape from the smaller outlet at higher presssure.

If anything messes up the aerodynamics that are forcing the air into the compressor, the high pressure air inside the pipe does what it really wants to, which is escape from both ends as fast as possible. The result is a bang, usually flames coming out of both ends of the engine at once, and internal mechanical damage that can range from negligible to catastrophic.

If the damage is negligible, the stable flow pattern may recover, or it may try to recover and produce repeated surges and bangs at a frequency of around one per second until something breaks. If the engine was running at high power, suddenly reducing the air flow while still pumping the same amount of fuel into the combustor is also not good news...
 
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  • #14
I understand it better now...the simple analogy of pipe flow is really helpful..
 
  • #15
Hi...i thought of an analogy(for the whole compressor as a whole)...not sure if its correct..
A stalled compressor is like an automobile pushing hard against a fixed wall...the wall won't allow the vehicle to move...but still if we continue to push, the engine heats up badly and does no useful work...
now in place of the engine we've the compressor which is trying hard to rotate the turbine...but since it is stalled, it would provide no useful work and just get heated up...
Does it sound ok, guys?
 
  • #16
koolraj09 said:
now in place of the engine we've the compressor which is trying hard to rotate the turbine...
That's back to front. The turbine is driving the compressor.
 
  • #17
Got that wrong...so the effect of stall (in above analogy) would be that the turbine is driving hard the compressor and in the process gets heated up.
 

1. What is a gas turbine compressor stall?

A gas turbine compressor stall occurs when the airflow through the compressor blades becomes disrupted, resulting in a sudden decrease in compressor performance and potential damage to the engine. This disruption can be caused by a variety of factors, such as high ambient temperatures, inlet pressure fluctuations, or foreign object debris.

2. How does a gas turbine compressor stall affect engine performance?

A gas turbine compressor stall can significantly impact engine performance. It can result in a decrease in thrust, power, and efficiency, as well as an increase in fuel consumption and emissions. In severe cases, it can lead to engine shutdown and potentially dangerous situations for the aircraft or other applications that use gas turbines.

3. What are the warning signs of a gas turbine compressor stall?

Some common warning signs of a gas turbine compressor stall include a decrease in engine speed and power, abnormal vibrations or noises from the engine, and an increase in exhaust gas temperature. These indicators can also be accompanied by a loss of thrust and increased engine drag.

4. How can gas turbine compressor stalls be prevented?

Gas turbine compressor stalls can be prevented through proper maintenance and monitoring of the engine. Regular inspections and cleaning of the compressor blades can help remove any potential debris or buildup that could disrupt the airflow. Additionally, engine monitoring systems can detect and warn of potential stall conditions, allowing for corrective actions to be taken before a stall occurs.

5. What are the consequences of a gas turbine compressor stall?

The consequences of a gas turbine compressor stall can range from minor performance issues to catastrophic engine failure. In addition to the impact on engine performance and efficiency, a stall can also cause damage to the compressor blades and other engine components. In some cases, a stall can lead to a complete engine shutdown, which can be dangerous for aircraft and other applications that rely on gas turbines for power.

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